1. Field of the Invention
The present invention relates to a liquid-crystal display device which is excellent in light utilizing efficiency and which provides a brilliant display easy to see, and a light pipe which can be used for forming the liquid-crystal display device.
The present application is based on Japanese Patent Application No. Hei. 11-111756, which is incorporated herein by reference.
2. Description of the Related Art
There is investigation of a liquid-crystal display device which is used both in a reflection and a transmission mode so that the device can be visually recognized in use of the transmission type liquid-crystal display device in a dark place, or the like, by addition of an illuminator while the merit of a reflection type liquid-crystal display device of small power consumption is used widely. For example, there have been proposed a liquid-crystal display device using a semi-transmission type reflection plate, a liquid-crystal display device in which a back light used in a transmission type liquid-crystal display device is provided as a front light on the visual recognition side of liquid-crystal cells, and so on.
The system utilizing such a semi-transmission type reflection plate, however, had a disadvantage that the system in either mode was inferior in brightness to the reflection or transmission type device for exclusive use because light was separated into reflected and transmitted light by a half-mirror effect. There was a proposal to make an improvement by use of a reflection polarizer for reflecting polarized light selectively so that the sum of reflectivity and transmissivity was able to exceed 100%. However, there were problems in that the light utilizing efficiency in a transmission mode was reduced to be not higher than 50% because of absorption by a light absorber disposed for preventing both display inversion between reflection and transmission and emphasis of a black display, and display was hard to see in the evening twilight in either mode. On the other hand, there was a problem in that the front light system was apt to make a display darker in a transmission mode than the general transmission type liquid-crystal display device because light went to light-crystal cells, or the like, and came back. Accordingly, an injury of a light pipe or a contaminant thereon became conspicuous as a bright spot, and display contrast was lowered by leakage of light from an upper surface of the light pipe.